1. Field of the Invention
The present invention relates to a semiconductor device, and, more particularly, to a multi-layer film having an improved interface characteristic for a thin film structure, a capacitor using the multi-layer film as a dielectric, and methods for fabricating the multi-layer film and the capacitor.
2. Description of the Related Art
Multi-layer films may be employed in semiconductor devices to obtain required device characteristics. For example, a multi-layer film obtained by stacking many different kinds of material layers may be employed as a dielectric film to increase the capacitance of a capacitor. A multi-layer film, such as an oxide/nitride/oxide (ONO) film or a nitride/oxide (NO) film, can be used as a dielectric film.
Methods of stacking new dielectric materials in composite manner have been suggested for the increase of the capacitance of capacitors, required as semiconductor devices become more highly integrated.
The hetero junction interface characteristic between different kinds of material layers forming a multi-layer film may be poor, however, because the different kinds of material layers have different interaction parameters to each other. When a material is deposited on a layer of material having an interaction parameter different from the deposited material, the deposited material may be deposited unevenly.
For example, a deposited of material may be deposited in the form of island growth, as shown in the schematic views of FIGS. 1 and 2 showing this mechanism of deposition. Referring to FIG. 1, when an upper material layer 20 having a different interaction parameter from that of a lower material layer 10 is deposited on layer 10, layer 20 grows out of nuclei formed by nucleation in the form of islands which stand apart from each other due to a hetero junction interface characteristic. Since the interaction parameters of layers 20 and 10 are different, the mechanism in which layer 20 nucleates from certain nucleation sites on layer 10 is applied prior to a uniform deposition mechanism in order to decrease surface energy. This deposition mechanism may be applied when layer 10 is aluminum oxide (Al2O3) and layer 20 is titanium oxide (TiO2).
Referring to FIG. 2, in the upper material layer 20 in which nuclei are grown into islands, the islands meet with each other and grow into a coalesced form during deposition. Accordingly, the deposited upper material layer 20 has a very coarse or rough surface topology. As the upper material layer 20 is deposited thinner, the topology of the surface of the upper material layer 20 becomes coarser or rougher. In other words, the thickness variation of the upper material layer 20 is very nonuniform. Thus, the film characteristic of the upper material layer 20 is also very nonuniform.
Various defects may result from the film characteristic of one among the material layers forming a multi-layer film being nonuniform. For example, if one of the material layers forming a multi-layer film shows large variation in its thickness, the thickness of the entire multi-layer film may be nonuniform. When a multi-layer film is used as a dielectric, the nonuniform thickness of a material layer of the multi-layer film influences the overall dielectric constant and causes the overall dielectric constant of the multi-layer film to be nonuniform. The nonuniform dielectric constant may degrade the characteristics of a capacitor.
It is an advantage of the present invention to provide a multi-layered film having improved uniformity.
According to another aspect of the present invention, a multi-layer film for a thin film structure, the multi-layer film comprises a first layer including a first element; a second layer including a second element different from the first element; and a third layer between the first and second layers, the third layer comprising the first and second elements, wherein a concentration of the second element, in the third layer, gradually varies from a portion of the third layer contacting with the first layer to a portion of the third layer contacting with the second layer, wherein the concentration of the second element is relatively higher in the portion of the third layer adjacent to the second layer.
According to yet another aspect of the present invention, there is a method for fabricating a multi-layer film for a thin film structure. The method comprises forming an intermediate layer on a first layer having a first element; and forming a second layer on the intermediate layer, the second layer comprising a second element different from the first element, wherein the intermediate layer is comprised of both the first and second elements, wherein a concentration of the second element, the intermediate layer, gradually varies from a portion of the intermediate layer contacting with the first layer to portion of the intermediate layer contacting with the second layer so that the concentration of the second element is relatively high in the portion of the intermediate layer adjacent to the second layer.
According to yet another aspect of the present invention, there is a capacitor of a semiconductor device. The capacitor comprises a first electrode on a semiconductor substrate; a multi-layer film configured as a dielectric on the first electrode, the multi-layer film including a first layer including a first element, a second layer including a second element different from the first element, and a third layer between the first and second layers, the third layer comprising the first and second elements, wherein a concentration of the second element, in the third layer, gradually varies from a portion of the third layer contacting with the first layer to a portion of the third layer contacting with the second layer, wherein the concentration of the second element is relatively higher in the portion of the third layer adjacent to the second layer; and a second electrode on the multi-layer film.
According to yet another aspect of the present invention, there is a method for fabricating a capacitor of a semiconductor device. The method comprises forming a first electrode on a semiconductor substrate; forming a multi-layer film on the first electrode as a dielectric, the multi-layer film including a first layer including a first element, a second layer including a second element different from the first element, and a third layer between the first and second layers, the third layer comprising the first and second elements, wherein a concentration of the second element, in the third layer, gradually varies from a portion of the third layer contacting with the first layer to a portion of the third layer contacting with the second layer, wherein the concentration of the second element is relatively higher in the portion of the third layer adjacent to the second layer; and forming a second electrode on the multi-layer film.